Crust breaker for aluminum fusion electrolysis cells

ABSTRACT

A slag crust breaker for aluminum fusion electrolysis cells is supported on a trolley carriage of a semi-portal crane, and comprises: a swingable, horizontally directed impact beam; pneumatic impact tool means hinged to the free end of the impact beam; an adjustable pneumatic driving device for driving the impact beam; a pneumatic control device for controlling the hold of the impact tool means in its vertical position; and a torsion device coupled to the impact tool means for deviating the tool about the axis of the impact beam when a predetermined lateral obstacle during the operation of the breaker occurs.

United States Patent Schaper et al.

CRUST BREAKER FOR ALUMINUM FUSION ELECTROLYSIS CELLS lnventors: Hans Schaper; Kurt Springer, both of Rheinfelden, Germany; Edgar Kyburz, Richards Bay, Empageni, Natal, South Africa Swiss Aluminium Ltd., Chippix, Switzerland Filed: Apr. 6, 1970 Appl. No.: 25,750

Assignee:

Int. Cl ..C22d 3/02, C22d 3/12 Field of Search ..204/67, 243 R; 225/103 References Cited UNITED STATES PATENTS 12/1960 Samhammer et a1. ..262/13 51 May 23, 1972 FOREIGN PATENTS OR APPLICATIONS Primary ExaminerJohn H. Mack Assistant ExaminerD. R. Valentine Attorney-Emest F. Marmorek ABSTRACT A slag crust breaker for aluminum fusion electrolysis cells is supported on a trolley carriage of a semi-portal crane, and comprises: a swingable, horizontally directed impact beam; pneumatic impact tool means hinged to the free end of the impact beam; an adjustable pneumatic driving device for driving the impact beam; a pneumatic control device for controlling the hold of the impact tool means in its vertical position; and a torsion device coupled to the impact tool means for deviating the tool about the axis of the impact beam when a predetermined lateral obstacle during the operation of the breaker occurs.

9 Claims, 21 Drawing Figures Patented May 23, 1972 15 Sheets-Sheet l Patented May 23, 1972 3,664,946

15 Sheets-Sheet 2 Patented May 23, 1972 3,664,946

15 Sheets-Sheet 4 Fig.5

Fig.4

Patented May 23, 1972 3,664,946

15 Sheets-Sheet 5 Patented May 23, 1972 15 Sheets-Sheet 6 Patented May 23, 1972 3,664,946

15 Sheets-Sheet 7 Fig. 8

Patented May 23, 1972 3,664,946

15 Sheets-Sheet 8 Patented May 23, 1972 15 Sheets-Sheet 9 Patented May 23,1972

l5 Sheets-Sheet 10 Patented May 23, 1972 15 Sheets-Sheet 11 Patented May 23, 1972 15 Sheets-Sheet 12 Patented May 23, 1972 15 Sheets-Sheet 155 Patented May 23, 1972 15 Sheets-Sheet 14 CRUST BREAKER FOR ALUMINUM FUSION ELECTROLYSIS CELLS This invention relates generally to slag crust breakers and, more particularly, to slag crust breakers of the type which automatically crash the slag crust on the fused electrolyte in a series of aluminum fusion electrolysis cells.

For a long time, the slag crust breaking operation in electrolysis cells has no longer been carried out manually, but is made mechanically by movable, pneumatically driven crust breakers. Recently, such mechanical crust breakers have also been provided with an alumina feeding equipment to insure a complete fusion furnace attendance, and such complex automatic crust breakers will, in the following description, be called furnace manipulators.

Known mechanically operated movable crust breakers are designed in various types. For example, they are mounted on a steerable carriage, or supported on movable frameworks such as semi-portal cranes, portal cranes or bridge cranes that are adapted for travelling above a row of electrolysis cells. In these prior art structures, the crust breaker usually comprises a vertical impact beam that is hinged or fixedly suspended at its top end to a movable support, and at its bottom end a pressure air cylinder with an impact tool are operatively mounted.

The disadvantage of this known structure resides in the fact that if the crust breaking operation is to be performed near the end sides of the electrolysis cell, there is no possibility to underrun the conduits for anode current extending along the center line of the cell. The slag crust in the middle area of the end sides has remained, therefore, intact. There are also known crust breakers with horizontally directed impact beams. Nevertheless, due to the prior art fixed arrangement of the impact tool on the horizontal impact beam, the crust breaking operation is unsatisfactory. In the breaking operation, for example, the impact tool often impinges against slag layer portions having different, greater hardness; or the tool may abut against the wall of the cell which is built with brick and covered with solidified electrolyte. Such rigid obstacles act, during the advance of the crust breaker, in horizontal direction of the impact tool. Excess lateral pulses of force may cause damage of the tool or even of the electrolysis cell.

To avoid these detrimental effects of lateral forces in the transverse direction to the longitudinal axis of the cell, U.S. Pat. No. 3,372,106 describes means that decline the vertically arranged impact beam in this transverse direction. The beam is kept in an operative vertical position by a horizontally acting spring loaded pushing rod so that predetermined lateral forces may decline the beam by overcoming the tension of this pushing rod. The holding force, however, is a function of fixed parameters of the spring and cannot be readily adjusted to changed operational conditions.

If the lateral or horizontal forces are acting in the direction of the longitudinal axis of the cell, the declination of the tool occurs automatically, since the impact beam in these prior art breakers is held in its vertical position by its own weight only. The disadvantage of such simple arrangement is in the fact that the declination takes place even at the occurrence of relatively minor lateral forces. Consequently, if slag layer portions occur that have a different hardness and such case is frequent in the aluminum electrolysis process the impact tool will be deflected in the plane vertical to the impact beam, and the crust breaking action will be interrupted. In known crust breakers with horizontal impact beams, there are usually no means that would control the declination of the impact tool. The only exception is the construction as disclosed in the British Pat. No. 990,832, where a rotary breaking wheel supports a fixedly attached impact tool. The disadvantage is that the tool is declined at the occurrence of minute lateral forces and the crust breaking operation is thus impeded.

In the course of the operational period of the aluminum fusing electrolysis cells, which covers several months or even years, changes may result in the configuration of the electrolysis cells. For example, the bottom of the cell may sink or rise and, accordingly, the slag crust layer may be raised or lowered. In addition, the thickness of the slag layer may vary as a result of different operational regimes or of different properties of the alumina (aluminum oxide) employed. Such operative fluctuation may occur at any time independently of the age of the electrolyte alone. Due to this fact, the crust breakers which have a fixed length of strokes of the impact tool cannot be adjusted to such changed operational conditions and the tool does not penetrate throughout the crust, or penetrates too deep into the electrolyte, sometimes impinging even on the fused metal bath in the cell.

Alumina to be processed in the electrolysis cell is usually distributed on the slag crust in a layer which has a nonuniform thickness. As a consequence, the alumina layer is fed into the electrolyte during the slag crust breaking process at quantities that are not optimum for the operation of the electrolysis cell. For example, an excess amount of alumina may cause siltation of the bath, whereas an insufficient amount may deteriorate the efficiency of the cell.

If alumina is added disregarding the prescribed alumina content in the electrolyte, an optimum operational efficiency of the cell can never be attained. On the other hand, if a preliminary measurement of the electrolyte by means of an auxiliary probe has been introduced into the cell operation, the resulting equipment and maintenance becomes overcomplicated.

Furthermore, the known furnace manipulators do not enable a simultaneous attendance of both longitudinal and end sides of a rectangular cell. These prior art manipulators have been designed for attending first one row of longitudinal sides and, subsequently, the opposite row of longitudinal sides. In the same manner the breaking operation along the end sides must have been accomplished.

BRIEF SUMMARY OF THE INVENTION It is, accordingly, one of the objects of this invention to avoid the aforementioned drawbacks of prior art slag crust breakers.

It is another object of this invention to enable the crust breaking operation simultaneously at opposite halves of a row of the electrolysis cells.

Itis still another object of this invention to improve the efficiency of the operation of the electrolysis cell.

It is also an object of this invention to provide means for protecting the impact tool against damaging lateral forces. I

It is furthermore an object of this invention to provide means for preventing alumina from entering the electrolyte during the slag crust breaking operation.

Also, it is an object of this invention to secure a maximum working effect of the impact tool.

Furthermore, it is an object of this invention to improve alumina charging and discharging processes.

In accordance with the present invention, a slag crust breaking device for use in metal fusion electrolysis cells comprises a movable support to which one end of a horizontal impact beam is hinged, a tool assembly which is hinged to the other end of the impact beam so as to be movable about its hinge in a vertical plane substantially parallel to a longitudinal axis of the beam and which carries a tool, the assembly having an operative position in which the tool is substantially vertical and can be driven into the slag crust in use, drive means coupled between the movable support. and the impact beam to swing the beam up and down about its hinged end and thereby driving the tool repeatedly into the slag crust in use, an adjustment device for adjusting at least a lower limit of travel of the tool, and a control device coupled between the impact beam and the tool assembly for holding the assembly in its operative position by an adjustable holding force, the arrangement being such that when the tool is subjected to horizontal forces greater than a pre-set magnitude, dependent on the adjustable holding force, the tool can deflect horizontally and swing the assembly about its hinge against the adjustable holding force.

The fact that the impact beams are arranged horizontally makes it possible to break the slag crust all along the end edges of the electrolytic cell. The horizontal impact beam travels across under the anode electric leads. This allows the crust to be broken all the way across the cell.

The adjustment device for adjusting the lower limit of travel of the tool makes it possible to ensure that the tool always penetrates to the same depth through the crust, that is to say penetrates downwards to the same distance from the upper surface of the crust. The control device for holding to the tool assembly in its operative position is preferably a pneumatic device. The pre-set magnitude of the holding force can then be adjusted by operation of a pneumatic control system. In the use the magnitude of the holding force should be set so that the tool is not deflected by comparatively moderate horizontal thrusts but only when abnormally high thrusts are applied.

Preferably the crust breaker is equipped with a torsional spring device which allows the chisel to yield resiliently by pivoting against the influence of springs, about an axis which either coincides with or extends parallel to the impact beam axis.

Here again the stiffness of the action may be adjustable, so that the tool yields only when the applied horizontal thrust exceeds a specified maximum normal value.

The breaking of the slag crust along the end edges of the electrolytic cell may be considerably facilitated if the movable support is a trolley carriage which travels transversely across the cell axis.

A furnace manipulator preferably includes two crust breakers, each mounted on its own trolley carriage, the two trolley carriages travelling, for example towards or away from each other, transversely across the cell longitudinal axis. This allows the two sides of the cell to be served simultaneously, and also allows the crust to be broken along the end edges of the cell by a simultaneous double operation, starting from the middle of the edge. When the crust has been broken in one row of cells, the crust breaker can move to the next row of cells without it being necessary to rotate the furnace manipulator.

The crust breaker according to the invention preferably forms part of a furnace manipulator, each crust breaker having two alumina feeder tubes, one in front of and the other behind the tool, as seen in the direction of travel. This allows the crust breaker to break the crust while travelling in either longitudinal direction, along the sides ofthe cell.

Each crust breaker may then have two alumina scrapers, one in front of and the other behind the tool, as seen in the direction of travel. In front of the chisel the layer of alumina is scraped back, towards the side wall of the cell. Behind the chisel the alumina is pushed forward again, towards the middle of the cell, so as to distribute the alumina evenly, increasing the efficiency of the electrolytic process.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS For a better understanding of the invention, reference is made to the following description taken in conjunction with the figures of the accompanying drawings in which:

FIG. 1 is an elevational view, partly in section, of a furnace manipulator according to this invention, with two crust breakers disposed in an operative position within the electrolysis cell;

FIG. 2 is a sectional view taken along line 22 ofFIG. 1;

FIG. 3 is an elevational view, partly in section, of a modification of the furnace manipulator according to this invention;

FIG. 4 is a schematic elevational view, partly in section, of an undercarriage of the semi-portal crane in the furnace manipulator of this invention;

FIG. 5 is a side view of the undercarriage of FIG. 4, taken perpendicularly to the direction of its travel;

FIG. 6 is an elevational view, partly in section, of an alumina feeding device;

FIG. 7 is an orthographical fragmentary view of an adjustment device for the pneumatic drive of the impact beam in the crust breaker according to this invention.

FIG. 8 is a schematic elevational view, partly in section, of a pneumatic control device acting in the vertical plane of the impact beam for holding at a predetermined force the vertical working position of the impact tool;

FIG. 9 is a schematic sectional view of a fluid pressure distributing valve of the control device of FIG. 8 in an activated position for reducing the hold of the impact tool;

FIG. 10 is a side view, partly in section, of a torsion device for holding at a predetermined force in transverse direction the vertical working position of the impact tool;

FIG. 11 is a sectional view of the torsion device of FIG. 10, taken on line 11-11;

FIG. 12 is a fragmentary orthographical view of an alumina scraping blade;

F IGS. 13 to 17 are elevational views of an alumina scraping device at the following positions:

at the rest position (FIG. 13);

at the position after the withdrawal of alumina from the slag crust area to be broken (FIG. 14);

at a lifted position of the scraper blade near the rim of the electrolysis cell (FIG. 15);

at a lifted position of the scraper blade near the anode (FIG. 16); and

at an operative position in engagement with the alumina layer prior to the initiation of the proper scraping action (FIG.

FIG. 18 is a schematic plan view of a series of rectangular electrolysis cells with the indication of the operative steps in the crust breaking operation along the longitudinal sides of individual cells;

FIG. 19 is the view of FIG. 18 with indicated operational steps for the crust breaking operation along the end sides of the cells;

FIG. 20 is the view of FIG. 18 wherein another modification of the crust breaking process in a series of electrolysis cells is indicated; and

FIG. 21 is the view of FIG. 18 of still another modification of the crust breaking process.

DETAILED DESCRIPTION With reference to FIGS. 1 to 3, the furnace manipulator for attending aluminum fusion electrolysis cells 18, is mounted on a semi-portal crane 10 having a bridge 38 and two trolley carriages 57 supported for travel on the bridge 38. One end of the bridge 38 is guided on an elevated crane runway 11 for travel in the direction of longitudinal sides of the cell 18. The required support of the bridge 38 on the runway 11 provides movable stools 12 driven from a motor 14. The opposite end of the bridge 38, on the other hand, is supported on an undercarriage 13 which moves on the ground floor of the smelting plant. The undercarriage 13 is provided with rubber tires and has no separate driving means. As seen in FIG. 2, each of the movable stools 12 is driven by an electromotor 14 through a transmission gear 15 and travelling wheels 16.

The structure of fusion electrolysis cells 18 is generally known to persons skilled in the art and, for reasons of simplification, only such parts of the cell 18 are illustrated in a sectional view in FIGS. 1 and 3 that are relevant to the operation of the crust breaker according to this invention. Anodes 19 are attached by means of anode rods 20 and anode locks 21 to anode current conductors 22. The cathode connection is insured by a cathode bar 23 at the bottom portion of the cell wall. Alumina is dissolved in an electrolyte layer 24 and, by the effect of the electric current, alumina becomes electrolyzed and fused aluminum 25 settles on the bottom of the fusion tub or furnace 26. A slag crust 27 results from the solidified electrolyte and from the undissolved alumina. The uppermost layer is an alumina layer 28.

With reference to FIGS. 4 and 5, the undercarriage 13 is substantially built up of a parallelogram frame formed by a bifurcated link 29, by a guiding rod and by one arm of an elbow lever 33. The bifurcated link 29 is provided with projecting studs that are in engagement with counteracting springs 32. These springs 32 are situated in a holding member 31 which is secured to the bridge 38. The perpendicular arm of the elbow lever 33 supports an axle 34 upon which bearings 36 of the rubber tire wheels 37 are seated. The bottom end of the perpendicular arm is operatively coupled with an undercarriage relieving device 35.

The provision of two opposed crust breakers in a single furnace manipulating unit enables simultaneous crust breaking operation on two parallel lines in a row of electrolysis cells or in two rows of these cells. In the latter case it is necessary that the manipulator be capable of making a continuous U-turn at each end of respective rows. Conventional undercarriages with a rigid supporting frame having the disadvantage that considerable lateral stresses occur in the wheel bearings when the undercarriage enters or leaves this curved path. These stresses are due to the fact that the undercarriage cannot follow exactly the trajectory of the elevated runway 11 of the crane 10. In the furnace manipulator according to this invention, the aforementioned parallelogram frame eliminates the disadvantage of the prior art undercarriages, since the parallel linkage of the bifurcated link 29 and of the guiding rod 30 always maintains an upright position of the rubber wheels, even when the end of the bridge 38 performs a circular movement. The restoring springs 31 restore normal vertical position of the links of the parallelogram when the bridge 38 travels on a rectilinear path again.

As indicated by dotted lines in FIG. 1, an air compressor 39 with a driving motor 40 and an air chamber 41 are mounted directly on the crane bridge 38. These pressure air sources supply pressure to various pneumatic driving and control devices which will be described later.

Further installations on the crane bridge 38 are a storage container or hopper 42 for receiving, storing and discharging alumina; the hopper 42 has at its top portion a feeding pipe 43 and a ventilating filter 44. To discharge alumina 45 from the hopper 42 (FIG. 2), the alumina must be aerified first. For this purpose, the aerating bottom plates 46 are installed in the hopper 42. Each bottom plate 46 comprises an air permeable intermediate plate made of a fabric or of ceramic, for example. The aeration of alumina is accomplished in a known manner by feeding pressure air into a lock chamber 48. The excess pressure air passes through the alumina 45 and escapes through the filter 44 (FIG. 1) which retains carried alumina particles.

The aerified aluminum particles 45 are discharged in predetermined quantities by the aid of a dosing device 49 (FIG. 6) that includes a slide valve 50 communicating with a rotary dosing lock 51. The lock 51 is supported for rotation on an axle 51a, and it is driven by a controlled drive 52. The outlet opening of the lock 51 is coupled by a compression valve 53 to a discharging pipe 54 through which the aerified alumina flows into the electrolytic bath. In the embodiment as shown in FIG. 2, discharging pipes 54 are arranged in the direction of travel at each side of the impact tool 75. Consequently, it is possible to discharge alumina 45 into the electrolyte 24 in either direction of travel of the crane 10.

As the alumina storing and discharging devices 42, 49 and 54 are integral with the crane bridge 38 and do not participate in the transverse movements of the trolley carriages 57, the end sides of the electrolysis cells are not supplied with alumina during the crust breaking action at these end sides. For this reason, the dosing device is put out of operation by a suitable conventional control device (not shown). At the same time, the aluminum scrapers are contracted into their lifted rest position (FIG. 13).

It is necessary, of course, that the slag crust 27 be covered by a sufficient layer of alumina even at the end sides of the cell 18. This can be accomplished by increasing the amount of alumina at the corners in each cell and by spreading this excess layer portion along the end sides.

A dust proof switching box 55 is also fixedly mounted on the movable crane bridge 38. The box 55 contains pneumatic switching means for supplying pressure to respective driving and controlling devices of the furnace manipulator.

Two parallel trolley travel rails 56 are arranged lengthwise on the crane bridge 38 to guide and support travel wheels 58 of the trolley carriages 57. These trolley carriages can, therefore, be moved in transverse direction to the travel of the bridge 38, and they are driven independently one from another by motors 59 and by transmission gears 60 (FIG. 2). The movement of the trolley carriages 57 is equalized by means of rollers 61, rocking levers 62 and tension springs 63. The rollers 6] follow parallel bottom rails 64 that are attached to the bottom surface of the crane bridge 38. The two trolley carriages support, in addition to the proper crust breakers, further devices that are needed for the attendance of the fusion furnace. The entire furnace manipulator is designed so as to enable any desired pattern of the crust breaking operation, namely to penetrate the slag layer along any desired continuous or interrupted lines both at the longitudinal and at the end sides of a row of cells.

The control of the automatic travel of the furnace manipulator, as well as of the automatic charging and discharging of the hopper 42 is effected by a suitable conventional electronic control equipment that is connected in cooperation with the switching box 55. As shown by way of example in FIG. 1, the following electrical control devices are employed for the furnace manipulator according to this invention: a travel program transmitter 66 which is located outside the furnace manipulator and which transmits instructions for the travel program of the crane 10; a travel program receiver 67 disposed on each trolley carriage 57 to cooperate with the program transmitter 66.

A furnace program transmitter 68 is mounted near the crane travel rail 11 and cooperates with a receiver 69 to control the electrolysis cell 18. A mechanical sensing device for controlling the slag breaking action within the cells 18 comprises a sensing roller 70 and a limit switch 71 which is coupled with copying rails 72 and sensing switches 73. The sensing switches turn on or off the driving and controlling devices of the furnace manipulator.

The crust breaker that is supported by the trolley carriage 57 comprises basically a swingable horizontally directed impact beam 92, and swingable vertically directed impact tool means 74 with an impact tool 75 such as, for example, a chisel made of a self-hardening steel. The impact beam is driven for an oscillatory movement by a pneumatic drive 77. The striking range of the impact tool 75 can be adjusted by means of a stroke adjustment device 76 coupled to the pneumatic drive 77, as illustrated in greater detail in FIG. 7. As seen in FIG. 7, the cylinder of the pneumatic drive 77 is hinged between the impact beam 92 and the vertically adjustable part 78 of the stroke adjustment device 76. This part 78 is slidably arranged between a fork 79 that is welded between two side plates 82 integral with the body of the trolley carriage 57. The vertical adjustment is carried out by left-hand and right-hand threaded halves of a spindle 80. The spindle is locked in the set position by a lock nut 81.

The impact tool means 74 includes preferably a pneumatic hammer 83 with the impact tool 75. The hammer 83 is fastened in a swingable mounting bracket 84 which pivots about an axle 85 in the vertical plane of the impact beam 92. The vertical working position of the hammer 83 is adjustably insured by a pneumatic control device 86 (FIG. 8) which determines and controls the force that is necessary for overturning the hammer 83 about the axle 85 in the direction perpendicular to the longitudinal axis of the electrolysis cell. As a consequence, it is now possible to break the slag crust along the end sides of the cell and not only along the longitudinal ones, as is the case in prior art devices. The penetration of the slag layer in transverse direction to the longitudinal axis of the cell is extremely important to attain optimum working regime of the fusion furnace as well as to insure a high performance. By contrast to prior art devices, the novel swingable arrangement of the impact tool means 74 eliminates the damaging excess lateral stresses against the impact tool 75 which occur during the slag crust breaking operation and, at the same time, due to the action of the pneumatic control device, the tool 75 remains unaffected by insignificant lateral strains.

With reference to FIGS. 8 and 9, the pneumatic control device 86 comprises a pneumatic cylinder 87 with a piston 88 and a piston rod 89. The piston 88 divides the interior of the cylinder 87 into pressure space 90, and into counterpressure space 91. The pressure space 90 is connected via a conduit to a pressure source, whereas the counterpressure space 91 is normally connected with the outer atmosphere. At this position, the piston 88 sets and locks with a considerable force the impact tool means in its working vertical position, so that the penetration through the slag crust is facilitated. Only if a lateral counterpressure on the tool 75 exceeds the pressure in the space 90, the pneumatic hammer 83 may be overturned. In this manner it is insured that the tool 75 is not uselessly angularly displaced when minor lateral stresses occur and, therefore, that no disturbances take place in the crust breaking operation. As seen in greater detail in FIG. 8, the mounting bracket 84 has the shape of an elbow lever that is jointed to the end of the piston rod 89. The pressure space 90 communicates through a chamber 99 in the slidable piston of a pressure distributing valve 94 with a pressure air conduit 95. In an unactuated or rest condition of the valve 94, a tension spring 98 displaces the slidable piston 97 to its extreme right-hand position. A solenoid 96, counteracting the tension spring 98, is at that moment without current. In that rest position, pressure air from the conduit 95 enters space 90 in the cylinder 87 and displaces the piston 88 to its extreme left-hand position. The counterpressure space 91 is for the time being connected through the left-hand portion of the valve 94 with the outer atmosphere. The exact vertical position of the impact tool means 74 is determined by a limit stop 102 integral with the elbow lever bracket 84 and abutting against the end of the impact beam 92.

As soon as the tool 75 strikes against the slag crust 27, the resulting power pulse is converted by a suitable transducer into a control signal that actuates the solenoid 96 of the pressure distributing valve 94. The armature 103 which is integrally connected to the slidable piston 97 thus becomes actuated and displaces the piston 97 against the tension of the spring 98 to its extreme left-hand position in the valve 94 (FIG. 9). Pressure air from the conduit 95 can now enter via the annular chamber 99 both the pressure space 90 and the counterpressure space 91 of the cylinder 87. As a result, the pressures against the opposite piston surfaces 104 and 106 will neutralize the holding force of the piston 88. There remains only a certain residual force which is proportional to the difference between the larger surface 106 and the smaller surface 104. Although such a residual force is still capable of holding the pneumatic hammer 83 in its vertical position, lateral forces against the impact tool 75 which might damage the crust breaker cause the entire impact tool means 74 to tilt about the axle 85, and pressure air in the cylinder 87 now acts as a pneumatic cushion.

By contrast to conventional devices such as described, for example, in the DBR Pat. No. l,275,875 where the slag breaking hammer is arranged vertically on a vertically suspended impact beam the position of which is controlled by a horizontally acting piston, the position above the slag layer of the hammer 83 according to this invention may be controlled by a combined action of a horizontally directed impact beam with the transverse movement of the trolley carriage 57 that may advance in the direction of the end walls of the cell 18 as far as the longitudinal center line where the breaking operation is initiated and proceeds toward the rim of the cell. By starting the movement of the crane bridge 38, the operation of the tool 75 may continue without any interruption along the longitudinal tire length of the line of striking, and that no portions of this line remain unbroken.

In the aforementioned known devices (DBR Pat. No. 1,275,875), a vertically hinged impact beam maintains its vertical position by it own weight only. It can, therefore, be inclined even by relatively small lateral forces, and for this reason it cannot work faultlessly.

A torsion device 139, as shown generally in FIGS. 1 and 3, and in greater detail in FIGS. 10 and 11, eliminates the aforementioned disadvantage of conventional devices. The impact beam 92 may have the form of a torsion rod, so that the tool 75 is partially turned about the axis of the beam 92 when excess lateral forces start acting against the tool 75 in the direction of the longitudinal axis of the cell, namely in the direction of travel of the crane bridge 38.

In a more elaborate modification of this torsion device 139, the tool 75 is held in its vertical working position by two strong counteracting springs 107 (FIGS. 10 and 11). The axle for pivotally supporting the impact tool means 74 is secured to one end of a sleeve 108. The sleeve 108 is seated for free rotational movement on the impact beam 92. Two spring barrels 111 with springs 107 and plungers are fixedly arranged opposite each other on the second end of the sleeve 108. A rigid stud 109 projects radially from the impact beam 92 between the two counteracting springs 107 so that the beam 92 is resiliently held in an upright position. The tension of the springs 107 is adjustable by threaded plugs 112.

To insure an optimum operation of the fusion electrolysis cell it is necessary to prevent the non-uniformly distributed alumina layer on the slag crust from entering the electrolyte during the crust breaking operation. In the furnace manipulator of this invention, the alumina layer on the line of breaking is successively removed from the range of the tool 75 and is displaced toward the rim of the cell and toward the anode. For this purpose, pneumatically operated alumina scraping devices 113 are arranged on the trolley carriage 57 at each side of the impact beam 92, and are extendable as far as the anodes 19. The detailed structure and operation of the scraping device 113 will be explained with reference to F IGS. 12 to 17.

The proper scraping tool is a scraping blade 114 (FIG. 12) that is swingably supported on an axle 115 at one end of the scraping arm 116. Tension spring means 117 keep the scraping blade 114 in its normal operative position but permit an angular displacement of the blade about the axle 115 if a rigid obstacle happens in its path of movement. Referring now to FIG. 13, the scraper arm 1 16 is linked to a piston rod 121 ofa pneumatic piston which is situated in a pneumatic driving cylinder 119. This linkage has the form of a toggle joint linkage resulting from the jointed elbow lever 122. The position of this toggle joint determines the restricted rest position or the extended working position of the entire scraping device 1 13. The movement of the scraping device 113 is controlled by a driving pneumatic cylinder 123 having a piston 124 and a piston rod 125. The outer end of the piston rod 125 is jointed to the end of the scraping arm 1 16. The entire scraping device 113 is mounted on a rocker 126 which is pivotally supported on a fixed axle 127. The scraper blade 114 is put into and out of engagement with the alumina layer 28 by a combined action of the pneumatic cylinder 123 with the oscillatory movement of the piston 28 in a pneumatic cylinder 128 driving the rocker 126.

FIG. 14 shows the position of the scraping device 113 at the moment when the scraping step has been completed. The edge of the scraper blade 114 is to be found at the point 131 at the end of the operative trajectory 132 of the scraper blade 114, as marked by the dot and dash lines.

FIG. 15 illustrates the position of the scraping device 1 13 at the moment when the scraper blade 114 has been disengaged 

1. A slag crust breaking device for use in aluminum fusion electrolysis cells, comprising in combination: a movable support; a horizontally directed impact beam hinged at one end thereof to said movable support; a tool assembly hinged to the other end of said impact beam so as to be movable about its hinge substantially parallel to a longitudinal axis in a vertical plane of said impact beam; said tool assembly carrying a tool and having an operative position in which the tool is substantially vertical and can be driven into the slag crust in use; drive means coupled between said movable support means and said impact beam to swing said beam up and down about its hinged end thereby driving the tool repeatedly into the slag crust in use; an adjustment device for adjusting at least a lower limit of travel of said tool; and a control device coupled between said impact beam and said tool assembly for holding said assembly in its operative position by an adjustable holding force the arrangement being such that when said tool is subjected to horizontal forces greater than a pre-set magnitude, dependent on the adjustable holding force, the tool can deflect horizontally and swing said tool assembly about its hinge against said adjustable holding force.
 2. The device according to claim 1 wherein said impact tool means is resiliently supported for a rotary movement about the longitudinal axis of said impact beam whereby said tool can deflect in response to horizontal forces parallel to a transverse axis of said beam.
 3. A device according to claim 2, in which the beam includes a sleeve which is rotatable about the longitudinal axis of the beam relatively to the end of the beam hinged to the movable support and to which the tool assembly is hinged, and pair of counter-acting spring means secured to the sleeve, and a lug projecting from the beam between the counter-acting spring means and rigid with the hinged end of the beam to hold with an adjustable force the tool assembly in its operative position.
 4. The device according to claim 1 wherein said movable support means comprises a first movable member driven for travelling in a first direction, a second movable member movably suspended on said first movable member for travelling in a second direction transverse to said first direction whereby said impact beam is hinged to said second movable member.
 5. The device according to claim 1 wherein said tool assembly is mounted on a rocker, said rocker being hinged to said impact beam.
 6. The device according to claim 1 further comprising metal ore hopper means, ore discharging means arranged on both sides of said impact tool assembly in the direction of its travel, said hopper means being located on said movable support means, and communicating with said metal ore discharging means.
 7. A device according to claim 1, in which the adjustment device for adjusting the lower limit of travel of the tool is coupled between the movable support and the drive means for swinging the beam about its hinged end.
 8. A device according to claim 1, in which the control device coupled between the beam and the tool assembly is pneumatically operable and includes a fluid pressure distributing valve, the arrangement being such that during each working stroke of the tool, the control device provides a full holding force until the moment of impact of the tool against the crust and a reduced holding force after the tool has penetrated the crust.
 9. A device according to claim 1 wherein said movable support includes a crane bridge movable in the direction of the longitudinal axis of said electrolysis cell; said crane bridge supporting a trolley carriage operable for movement in a direction transverse to said longitudinal axis, said crust breaking device being mounted on said trolley carriage thereby enabling it to break the slag crust also along the end walls of said electrolysis cell. 